In the production of some valves, it is necessary to provide a valve seat at a location in the valve body which is very difficult to reach from the exterior of the valve. For example, such a valve seat might face toward one end of the valve body passage, but be located at a position relatively distant from that end of the passage.
Many valves of this type are required to have a valve seat with high wear resistance. For example, a valve of this type might have to withstand liquid sodium such as is used in liquid metal breeder reactors at pressures near 375 PSI and temperatures greater than 200.degree. F. It is imperative therefore that the valves be 100 % defect free. In such cases, it is often desired to use Stellite, 6, a chrome-cobalt-tungsten material, to form such a valve seat; but, it is impractical and/or impossible to make an entire valve body from such materials due to cost and other factors.
Consequently, such valves have been produced from a suitable ferrous or non-ferrous material by forming a welding surface at a predetermined location within the valve body. For example, the entire valve body, including the welding surface, might be formed from stainless steel. Then, a technician installed a plurality of continuous Stellite 6 beads about the welding surface until an enlarged seat-forming member had been created. Then, the plurality of beads would be machined to form the desired valve seat.
This formation of an oversized deposit for later machining was time consuming, tedious, and severely susceptible to defects. In other words, if the welder made a single mistake in laying down the plurality of beads, the entire valve body was destroyed. It has been found that such errors occurred in the range of 50% of the time. As stated previously, it is necessary that each valve be substantially 100% defect free. In order to insure such perfection, ultrasonic testing and liquid penetrant examination may be accomplished, along with visual study of the valve seat.
Although such wear-resistant seat could be formed by brazing within the stainless steel body, such a bond cannot be tested except visually and there is no guarantee that the valve will withstand the temperatures and pressures required. Such a seat could be formed by inertia welding the wear-resistant material directly into the valve body, but the amount of rotary energy and the upsetting forces required to achieve such a weld make such a process impractical in terms of satisfactory production of usable, undamaged valves.
Accordingly, it has become imperative to provide a method which can be utilized to consistently produce such defect free valves at a relatively rapid rate with little or no construction failure.